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Diabetes, Vol 49, Issue 9 1543-1551, Copyright © 2000 by American Diabetes Association
Effect of hypoglycemia on amino acid and protein metabolism in healthy humans
A Battezzati, S Benedini, A Fattorini, L Piceni Sereni and L Luzi
Department of Medicine, Istituto Scientifico H San Raffaele, Milan, Italy.
In response to hypoglycemia, healthy individuals rapidly antagonize insulin
action on glucose and lipid metabolism, but the effects on protein
metabolism are unclear. Because amino acids are an important substrate for
gluconeogenesis and a fuel alternative to glucose for oxidation, we
evaluated whether hypoglycemia antagonizes the hypoaminoacidemic and the
antiproteolytic effects of insulin and changes the de novo synthesis of
glutamine, a gluconeogenic amino acid. To this purpose, in 7 healthy
subjects, we performed 2 studies, 3.5 h each, at similar insulin but
different glucose concentrations (i.e., 4.9 +/- 0.1 mmol/l [euglycemic
clamp] or 2.9 +/- 0.2 mmol/l [hypoglycemic clamp]). As expected,
hypoglycemia antagonized the insulin suppression of glucose production
achieved in euglycemia (from 21 +/- 15 to 116 +/- 12% of basal, P <
0.001), the stimulation of glucose uptake (from 207 +/- 28 to 103 +/- 7% of
basal, P < 0.01) and the suppression of circulating free fatty acids
(from 30 +/- 5 to 80 +/- 17% of basal, P < 0.001). In contrast,
hypoglycemia increased the insulin suppression of circulating leucine (from
63 +/- 1 to 46 +/- 2% of basal, P < 0.001) and phenylalanine (from 79
+/- 3 to 64 +/- 3% of basal, P < 0.001) concentrations. Hypoglycemia did
not change the insulin suppression of proteolysis (from 79 +/- 2 to 82 +/-
4% of basal, P < 0.001). However, hypoglycemia doubled the insulin
suppression of the glutamine concentrations (from 84 +/- 3 to 63 +/- 3% of
basal, P < 0.01) in the absence of significant changes in the glutamine
rate of appearance, but it also caused an imbalance between glutamine
uptake and release. This study demonstrates that successful
counterregulation does not affect proteolysis. Moreover, it does not
increase the availability of circulating amino acids by de novo synthesis.
In contrast, despite the lower concentration of circulating amino acids,
hypoglycemia increases the uptake of glutamine that can be used for
gluconeogenesis and as a fuel alternative to glucose.

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Copyright © 2000 by the American Diabetes Association.
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